Electrolytic refining of tin



Patented Mar. l8, 1924.

NIT

HARRY n. ALEXANDER, or WESTFIELD SMELTING- AN D BEFININ G COMPANY, NEW JELECTROLYTIC REFINING OF Tm.

No Drawing. Application filed December 30 -1920, Serial No. 434,124.Renewed October 26,1923. I

To all whom it may concern: 7 Be it known that I, HARRY H. ALEXANDER,

a citizen of the. United States, and resident of \Vestfield, in thecounty of Union and State of New Jersey, have invented certain new anduseful Improvements in Electroing is a'specification.

The invention relates to certain new and useful improvements in theproduction of an electrolytically refined tin from impure tinanodes andthe present disclosure constitutes an improvement over the disclosure inthe patent to R. L. \Vhitehead, #1,157,- 830, October 26, 1915.

It is suggested in this patent that in the lytic Refining of Tin, ofwhich the followelectrolytic refining. of tin containing lead,

an 'amount of sulphuric acid be added to the electrolyte, whichcontains'metallic tin dissolved in hydrofluosilicic acid, in an amountsufiicient to convert the lead present into lead sulfatewhiclrisinsoluble in the electrolyte. The patentee suggests the employment in atwenty-per cent solutiou'of hydrofluosilicic acid to insure thecontinued maintenance of the electrolytic decom'positiomof the tinduring the refining operation.

Under some conditions this electrolyte did not prove entirelysatisfactory especially when an addition agent, such as glue was added.For instance, ipolariaation would occur, necessitating the re uentremoval of the cathode plates, silica iO would deposit on the anodes andwhen attempts were made to heat this electrolyte as suggested in theapplication of Stack Serial N 0. 434,114, filed under even date therewould result a loss of acid as silicon fluoride (SiF,,) It was a usualpractice in using the patented electrolyte to line the tanks with tarpape'rand pitch which rapidly deteriorated especially when cresylic acidwasused as one of the addition agents in the nianner suggested in.

the application of Frank C. Mathers, Serial No. 257,700, filedOctoberll, 1918. I

,The primary object of the present invention is to provide anelectrolytewhich will effectively and continuously dissolve the tin,

which will precipitate-the lead'from the anode, which will prevent theformation of the basicsalts of tin, will render the anode entirelysoluble, prevent polarization and permit the use of a tank linin whichwill be substantially unaffected by t e contents of the tank.

Incidentally other objects of the invention n-nw JERSEY, As'smiron Toamnnronn or NEW YORK, N. Y., a oonronarroiv or is to attain high currentefliciency and to obtain a smooth, dense, tinof high purity.

I attain this invention broadly simply by adherent deposit of changingthe character of the electrolyte de fined in the \Vhitehead patent,above identified, from a hydrofluosilicic acid basis to a sulphuric acidbasis. Instead of using merely sufiicient sulphuric acid to unite withthe lead present in the electrolyte a materially excessive amount ofsulphuric acid is used. Further'and mainly for the purpose of featuringeconomy in the use of the relatively expensive hydrofluosilicic acid,the contents of this acid in theelectrolyte is reduced with beneficialeffect. While it is within the scope of this disclosure to suggest anyamount of sulphuric acid in excess of the amountnecessary to precipitatethe lead it has been found in practice that six to eight per cent offree sulphuric acid gives the best conductivity and anode corrosion,

but-this proportion is only suggestive of ranged preferably in batterieswith the impure tin usually .cast in anodes and each operativelyassociated in a lead lined'tank with a cathode usually formed of tin. Adirectv current of suitable voltage and of about eight amperes persquare foot of cathode surface is passed from the impure tin as anodesto the cathodes through the sulphuric hydrofluosilicic acid electrolyteas is well known in the racticing of such processes.- The tin isdissolved from the anodes into the electrolyte and deposited out of the"electrolyte upon the cathode plates.

The impurities usually found in such tin will not dissolve from theanode in the presence of the large .excess of tin present and the leadwhich dissolve'sis precipitated as sulfate and appears as a' slime whichis later subjected to other treatments in order a to retain itsvalues.

With this sulphuric acid electrolyte a was possible to use lead linedtanks without anger of destruction from the electrolyte.

The presence of the large excess of sulphuric acid prevents any solventaction of the sulphurous acid on the lead and the resence of thehydrofluosilicic acid even in t 1e reduced 1 proportions hereinsuggested prevented the formation of basic salts of tin, rendered theanode soluble and prevented polarization.

, of suitable voltage and amperage from the impure tin as an anode to acathode through an electrolyte which is a solvent of tin and lead andprotecting the electrolyte from contamination by lead, by incorporatingwith the electrolyte an agent which will combine with the lead to forman insoluble compound, said agent being present in an amount materiallyin excess of the amount necessary to unite with all the lead present inthe elec-.

trolyte.

2. In the electrolytic refining of impure tin containing lead, themethod of refining tinwhich consists in passing an electrolytic 4current of" suitable voltage and amperage from the impure tin as ananode to a cathode through a solution of hydrofluosilicic ac dcontaining an amount of sulphuric acid greatly in excess "of ,the amountsufli-' cient to combine with the lead in the electro- I lyte to formlead sulphate.

3. In the electrolytic refining of impure tin, the method of preventingcontamination of the tin deposited from the impure tin anode upon thecathode, which consists in employing as the electrolyte a solution oftin All in hydrofluosilicic acid together with a quan tity of sulphuricacid in excess of the amount suflicient-to convert thelead of thedissolving anode into-lead sulphate thereby to leave some free sulphuricacid in the electrolyte. I v

4:. The process for the refining of impure tin, which comprises passingan electrolytic current of suitable voltage and amperage from a tinanode to a; cathode through a solution of hydrofluosilicic acidcontained in a lead lined tank and addin'gto the solution an agent whichwill protect the tank lining from the solvent action of thehydrofluosilicic acid.

5. An electrolyte for the deposition of tin free from lead, comprisingan electrolytic solution of tin in hydrofluosilicic acid containing alarge amount of sulphuric acid, whereby, upon the passage of a currenttherethrough from an impure tin anode containing lead to a cathode, thetin will be dissolved from ,the anode and deposited on the cathodewithout contamination with lead and in the presence of an excess of thesulphuric acid.

6. In the electrolytic refining of impure tin containing lead, themethod of refining tin which consists in passing an electrolytic currentof suitable voltage and amperage t'roln the impure tin as'an anode to acathode through a solution of hydro-.'

fluosilicic acid three-to five per cent and free sulphuric acid six toeight per cent.

7. In the electrolytic refining of impure tin containing lead,the methodof refining tin which consists in passing an electrolytic current ofsuitable voltage and amperage from the impure tin as an anode to acathode through a solution of hydrofiuosilicic acid three to five percent and free sulphuric acid six to eight per 'cent and in the prescence' of an addition agent.

8. In the electrolytic refining of impure tin containing lead, themethod of refining tin which consists in passing an electrolytic currentof suitable voltage and amperage I from the'impure tin as an anode to acathode through a solution of hydrofluosilicic acid threeatqfive percent and free sulphuric acid six to eight per cent and in the presenceof .cresylic acid and glue.

SIgned at Maurer, in the county of Middlesex and State of New Jerseythis twentvsecond day of December, A. I); 1920. i

. HARRY II. ALEXANDER.

